Between Your Brain + Eyes
BETWEEN YOUR BRAIN + EYES
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MIT Press Published in 2014 One Rogers Street Cambridge MA 02142-1209 Tel: (617) 253-5646 Fax: (617) 258-6779 info @ mitpress.edu www.mitpress.mit.edu All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage and retrieval system, without prior permission in writing from the publisher.
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This book is dedicated to my family. You are what truly inspires me.
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Understanding Optical Illusion [Historical Examples and Evidence]
Breaking Down Optical Illusion [The Types and Categories that Influence]
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The Visual Mechanism [How We See and the Eye’s is Trained to See]
Mind Power [Optical Illusion’s Affect on the Brain]
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INTRODUCTION
Eventually one of the results of application to the analysis and measurement of the color, vision, lighting and light phenomena is a firmly entrenched conviction of the inadequacy of physical measurements as a means for representing what is perceived. Physical measurements have supplied much of the foundation of knowledge and it is not a reflection upon their great usefulness to state that often they differ from the results of intellectual appraisal through the visual sense. In other words, there are numberless so called optical illusions which must be taken into account. All are of interest; many can be utilized; and some must be suppressed. Scientific literature yields a great many valuable discussions from theoretical and experimental viewpoints but much of the material is controversial. The practical aspects of optical illusions have been quite generally passed by and, in as much as there does not appear to be a volume available which treats the subject in a condensed manner but with a broad scope, this small volume is contributed toward filling the gap.
glimpses of various aspects can be given in order to limit the text to a small volume. Some theoretical aspects of the subject are still extremely controversial, so they are introduced only occasionally and then chiefly for the purpose of illustrating the complexities and the trends of attempted explanations. Space does not even admit many qualifications which may be necessary in order to escape criticism entirely. The optical illusions discussed here are chiefly of the static type. Some of the latter border upon motion, others upon hallucinations, and still others produced by external optical media are optical illusions only by extension of the term. These exceptions are included for the purpose of providing glimpses into the border lands. It is hoped that this condensed discussion, which is ambitious only in scope, will be of interest to the general reader, to painters, decorators, and architects, and to all interested in light, color, and vision.
Here the complexity of this subject, which is extreme, it is well recognized, but an attempt toward simplicity has been made by confining discussions mainly to static optical illusions, by suppressing minor details, and by subordinating theory. In other words, the intent has been to emphasize experimental facts. Even these are so numerous that only the merest
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Understanding Optical Illusion [Historical Examples and Evidence]
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Optical Illusions are Everywhere Seeing is deceiving. Thus a familiar epigram may be challenged in order to indicate the trend of this book which aims to treat certain phases of optical illusions. In general, we do not see things as they are or as they are related to each other; that is, the intellect does not correctly interpret the deliverances of the visual sense, although sometimes the optical mechanism of the eyes is directly responsible for the optical illusion. In other words, none of our conceptions and perceptions are quite adequate, but fortunately most of them are satisfactory for practical purposes. Only a part of what is perceived comes through the senses from the object; the remainder always comes from within. In fact, it is the visual sense or the intellect which is responsible for optical illusions of the various types to be discussed in the following chapters. Our past experiences, associations, desires, demands, imaginings, and other more or less obscure influences create optical illusions. An optical illusion does not generally exist physically but it is difficult in some cases to explain the cause. Certainly there are many cases of errors of judgment. A mistaken estimate of the distance of a mountain is due to an error of judgment but the perception of a piece of white paper as pink on a green background is an error of sense. It is realized that the foregoing comparison leads directly to one of the most controversial questions in psychology, but there is no intention on the author’s part to cling dogmatically to the opinions expressed. In fact, discussions of the psychological judgment involved in the presentations of the visual sense are not introduced with the hope of stating the final word but to give readers an idea of the inner process of perception. Final word will be left to the psychologists but appears possible that it may never be formulated. A tree will appear longer when it is standing than when it is lying on the ground. Lines, areas, and masses are not perceived in their actual physical relations. The appearance of a colored object can also vary
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Figure 1.1 Is the pair horizontal line bowed or curved? In reality the two curved lines are parallel. They only appear to be curved because of the background.
considerably with its environment. The sky is not perceived as infinite space nor as a hemispherical dome, but as a flattened vault. The moon apparently diminishes in size as it rises toward the zenith. A bright object appears larger than a dark object of the same physical dimensions. Flat areas may appear to have a third dimension of depth. Optical illusions are so numerous and varied that they have long challenged the interest of the scientist. They may be so useful or even so disastrous that they have been utilized or counteracted by the skilled artist or artisan. The architect and painter have used or avoided them. The stage artist employs them to carry the audience in its imagination to other environments or to far countries. The magician has employed them in his entertainments and the camouflage used them to advantage in the practice of deception during the recent war. They are vastly entertaining, useful, deceiving, or disastrous, depending upon the viewpoint. Incidentally, a few so-called optical illusions will be discussed which are not due strictly to errors of the visual sense or of the intellect. Examples of these are the mirage and certain optical effects employed by the magician. In such cases neither the visual sense nor the intellect errs. In the case of the mirage rays of light coming from the object to the eye are bent from their usual straight-line course and the object appears to be where it really is not. However, with these few exceptions, which are introduced for their specific interest and for the emphasis they give to the “true” optical illusion, it will be understood that optical illusions in as
here in after discussed will mean those due to the visual mechanism or to errors of judgment or intellect. For the sake of brevity we might say that they are those due to errors of visual perception. Furthermore, only those of a “static” type will be considered; that is, the vast complexities due to motion are not of interest from the view point of the aims of this book. There are two well-known types of misleading perceptions, namely optical illusions and hallucinations. If, for example, two lines appear of equal length and are not, the error in judgment is responsible for what is termed an “optical illusion.” If the perceptual consciousness of an object appears although the object is not present, the result is termed an “hallucination” For example, if something is seen which does not exist, the essential factors are supplied by the imagination. Shadows are often wrought by the imagination into animals and even human beings bent upon evil purpose. Ghosts are created in this manner. Hallucinations depend largely upon the recency, frequency, and vividness of past experience. A consideration of this type of misleading perception does not advance the aims of this book and will be omitted.
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History of Optical Illusion The ancients sensed the existence or possibility of optical illusions is evidenced by the fact that they tried to draw and to paint. Although their inability to observe carefully is indicated by the absence of true shading. The architecture of ancient Greece reveals a knowledge of certain optical illusions in the efforts to over come them. However, the study of optical illusions did not engage the attention of scientists until a comparatively recent period. Not with standing this belated attention there is a vast scientific literature pertaining to the multitudinous phases of the subject; however, most of it is fragmentary and much of it is controversial. Some of it deals with theory for a particular and often a very simple case. In life complex optical illusions are met but at present it would be futile to attempt to explain them in detail. Furthermore, there have been few attempts to generalize and to group examples of typical phenomena in such a manner as to enable a general reader to see the complex fabric as a whole. Finally, the occurrence and application of optical illusions in various arts and the prominence of optical illusions on every hand have not been especially treated. It is the hope that this will be realized in the following chapters in so far as brevity of treatment makes this possible. Undoubtedly, thoughtful observers of ages ago would have noticed optical illusions, especially those found in architecture and nature. When it is considered that geometrical figures are very commonly of an illusory character it appears improbable that optical illusions could have escaped the keenness of Euclid. The apparent enlargement of the moon near the horizon and the apparent flattened vault of the sky were noticed at least a thousand years ago and literature yields several hundred memoirs on these subjects. One of the oldest dissertations upon the apparent form of the sky was published by Alhazen, an Arab astronomer from the tenth century. Figure 1.2 Rubin’s vase is a famous set of ambiguous or bi-stable two dimensional forms developed around 1915 by the Danish psychologist Edgar Rubin. These types of stimuli are both interesting and useful because they provide an excellent and intuitive demonstration of the figure ground distinction the brain can make perceptively.
Philosophers of the past centuries prepared the way toward an understanding of many complexities of today. They molded thought into correct form and established fundamental concepts and principles. Their chief tool was philosophy, the experimental attack being left to the scientists of the modern age. However, they established philosophically such principles as “space and time are not realities of the phenomenal world but the modes under which we see things apart.� As science became organized during the present experimental era, measurements were applied and there began to appear analytical discussions of various subjects including optical illusions. One of the earliest investigations of the modern type was made by Oppel, an account of which appeared in 1854. Since that time scientific literature has received worthy contributions dealing with optical illusions.
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Understanding Optical Illusions There are many facts affecting vision regarding which no theory is necessary. They speak for themselves. There are many equally obvious facts which are not satisfactorily explained but the lack of explanation does not prevent their recognition. In fact, only the scientist needs to worry over systematic explanations and theoretical generalizations. He needs these in order to invade and to explore the other unknowns where he will add to his storehouse of knowledge. A long step toward understanding is made by becoming acquainted with certain physical, physiological, and psychological facts of light, color, and lighting. Furthermore, acquaintance with the visual process and with the structure of the eye aids materially. For this reason the next two chapters have been added even at the risk of discouraging some readers.
A
Intermediate object going in down from the top.
Any visual perception which does not harmonize with physical measurements may be termed an “optical illusion.” Therefore, this term could include physical optical illusions obtained by means of lenses, mirrors and prisms and also optical illusions such as the mirage. It could also include the physiological illusions of light and color such as after images, irradiation, and contrast, and the psycho physiological illusions of space and the character of objects. In fact, the scope of the following chapters is arbitrarily extended to include all these aspects, but confines consideration only to “static” illusions.
B
In a more common sense, attention is usually restricted to the last group; that is, to the psycho-physiological illusions attending the perception of space and the character of objects although motion is often included. It should be obvious that no simple or even single theory can cover the vast range of optical illusions considered in the broad sense because there are so many different kinds of factors involved. For this reason explanations will be presented wherever feasible in connection with specific optical illusions. However, in closing this chapter it appears of interest to touch upon the more generally exploited theories of optical illusions of the type considered in the foregoing restricted sense. Hypotheses pertaining to optical illusions are generally lacking in agreement, but for the special case of what might be more safely termed “geometrical-optical illusions” two different theories, by Lipps and by Wundt respectively, are conspicuous. In fact, most theories are variants of these two systematic “explanations” of optical illusions.
A basic wire frame cube with no depth cues.
C
Intermediate object going in up from the bottom.
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Lipps proposed the principle of mechanical aesthetic unity, according to which we unconsciously give to every space form a living personality and unconsciously consider certain mechanical forces acting. Our judgments are therefore modified by this anthropomorphic attitude. For example, we regard the circle as being the result of the action of tangential and radial forces in which the latter appear to triumph. According to Lipps’ theory the circle has a centripetal character and these radial forces toward the center, which apparently have overcome the tangential forces during the process of creating the circle, lead to underestimation of its size as compared with a square of the same height and breadth. By drawing a circle and square side by side, with the diameter of the former equal to the length of a side of the latter, this optical illusion is readily demonstrated. Of course, the square has a greater area than the circle and it is difficult to determine the effect of this disparity in area.
Figure 1.3 The Necker Cube is an ambiguous line drawing. It is a wireframe drawing of a cube in oblique perspective, which means that parallel edges of the cube are drawn as parallel lines. When two lines cross, the picture does not show which is in front and which is behind. It can be interpreted two different ways. When a person stares at the picture, it will often seem to flip back and forth between interpretations.
Wundt does not attribute the optical illusion to a deception or error of judgment but to direct perception. According to his explanation, the laws of retinal image (fixation) and eye movement are responsible. For example, vertical distances appear greater than horizontal ones because the effort or expenditure of energy is greater in raising the eyes than in turning them through an equal angle in a horizontal plane. Unconscious or involuntary eye-movements also appear to play a part in many linear or more accurately, angular illusions, but certainly Wundt’s explanation does not suffice for all optical illusions although it may explain many geometrical illusions. It may be said to be of the “perceptive” class and Lipps’ theory to be of the “judgment” or “higher-process” class. As already stated, most of the other proposed explanations of geometrical illusions may be regarded as being related to one of these two theories. There is the “indistinct vision” theory of Einthoven; the “perspective” theory of Hering, Guye, Thiery, and others; the “contrast” theory of Helmholtz, Loeb, and Heyman; and the “contrast-confluxion” theory of Muller-Lyer. In order not to discourage the reader at the outset, theories as such will be passed by with this brief glimpse. However, more or less qualified explanations are presented occasionally in some of the chapters which follow in order to indicate or to suggest a train of thought should the reader desire to attempt to understand some of the numerous interesting optical illusions.
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Breaking Down Optical Illusion [The Types and Categories that Influence]
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Why Study Optical Illusions? Optical illusions, more appropriately known as visual illusions, involve visual deception. Due to the arrangement of images, effect of colors, impact of light source or other variable, a wide range of misleading visual effects can be seen. If you’ve ever struggled to see the hidden image in a single-image stereogram, you may have discovered that not everyone experience visual illusions in the same way. For some illusions, some people simply are not able to see the effect. Optical illusions fascinate us, challenging our default notion that what we see is real. They demonstrate that all our perception is illusion, in a sense incoming sensory information is interpreted, yielding the internal representation of the world. Therefore, after our eyes have filtered the visual input we need sound judgment of information in order to create our inner reality: “Your senses then you’ll have to trust, They’ll let you see what’s true and just, Should reason keep your mind awake”. What is an optical illusion? “I know it when I see one” could not be farther off the track, as the best illusions are the ones where a discrepancy from reality is not seen until one uses other modalities (eg. touch) or instruments (rulers, light meters). And even when we know that we are subject to an optical illusion, most illusory percepts still persist – a phenomenon called cognitive impenetrability. It is surprisingly hard to define illusion in a satisfactory way. According to the Merriam-Webster Online Collegiate Dictionary, an illusion is something that deceives or misleads intellectually; perception of something objectively existing in such a way as to cause misinterpretation of its actual nature. Is it only the playful child in scientists that drives them to study optical illusions? To some degree, yes, but illusions can also decide major sport events: referee judgments probably are affected by the flash lag effect, eg. when judging the spot where a tennis ball touched the ground. However, there are professional reasons as well: Optical illusions are particularly good adaptations of our visual system to standard viewing situations.
The Three Types of Optical Illusion 1
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Literal
Cognitive
Physiological
Create images that are different from the objects that make them.
Arise by assumptions about the existing world
The effects on the eyes or brain of excessive stimulation.
These adaptations are hardwired into our brains, and thus can cause inappropriate interpretations of the visual scene. Hence illusions can reveal mechanisms of perception. There are also some clinical conditions in which optical illusions play a major role, eg. organic psychoses, epileptic aura and migraine. Another often overlooked disorder is the Charles Bonnet syndrome: patients with a normal cognitive status but reduced afferent sensory input due to visual system pathology (eg. age-related macular degeneration) or with brainstem pathology experience visual hallucinations of various sorts. Finally, from a visual scientist’s point of view the Rorschach test is based on optical illusions or more precisely on the phenomenon that our brain is constantly looking for known patterns in random structures with low information content, called pareidolia. Some illusions are long known to mankind, eg. the waterfall illusion was mentioned by Aristotle: after staring at a waterfall for a couple of minutes neighboring objects seem to be shifting upwards. This was followed up by Lucretius, Purkinje and Addams who coined the term waterfall illusion. Recent evidence suggests that this motion aftereffect is not due to fatigue but rather due to a gain adjustment, an optimal adaptation to conditions.
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Physiological Illusions
Lateral Inhibition. A typical receptive field with an inhibitory surround is shown with a “Mexican hat” model, where excitation is shown by a peak and inhibition is shown by a surrounding valley. A single point stimulus generates the same pattern in the spatial distribution of evoked neural activity within the brain.
One Point Stimulus
Neural Activity
The Hermann grid illusion and Mach bands are two illusions that are best explained using a biological approach. Lateral inhibition, where in the receptive field of the retina light and dark receptors compete with one another to become active, has been used to explain why we see bands of increased brightness at the edge of a color difference when viewing Mach bands. Once a receptor is active it inhibits adjacent receptors. This inhibition creates contrast, a highlighting edges. In the Hermann grid illusion the gray spots appear at the intersection because of the inhibitory response which occurs as a result of the increased dark surround. Lateral inhibition has also been used to explain the Hermann grid illusion, but this has been disproved. More recent “empirical” approaches to optical illusions have had some success in explaining optical phenomena with theories.
Figure 2.1
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Two Point Stimulus
Neural Activity
Physiological illusions, such as the afterimages following bright lights, or adapting stimuli of excessively longer alternating patterns (contingent perceptual after effect), are presumed to be the effects on the eyes or brain of excessive stimulation or interaction with contextual or competing stimuli of a specific type brightness, color, position, tile, size, movement, etc. The theory is that a stimulus follows its individual dedicated neural path in the early stages of visual processing, and that intense or repetitive activity in that or interaction with active adjoining channels cause a physiological imbalance that alters perception.
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Figure 2.2 Hermann grid: This leads to a physiological mechanism: lateral inhibition, which has the effect of causing a bright surround to an area appear darker and, conversely, a dark surrounding will make an area appear much lighter.
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Cognitive Illusions Cognitive illusions are assumed to arise by interaction with assumptions about the world, leading to “unconscious inferences”, an idea first suggested in the 19th century by the German physicist and physician Hermann Helmholtz. Cognitive illusions are commonly divided into ambiguous illusions, distorting illusions, paradox illusions, or fiction illusions. Ambiguous images or reversible figures are optical illusion images which exploit graphical similarities and other properties of visual system interpretation between two or more distinct image forms. These are famous for inducing the phenomenon of multistable perception. Multistable perception is the occurrence of an image being able to provide multiple, although stable, perceptions. Classic examples of this are the rabbit/duck and the Rubin vase. Ambiguous images are important to the field of psychology because they are often research tools used in experiments. There is varying evidence on whether ambiguous images can be represented mentally, but a majority of research has theorized that they cannot be properly represented mentally. Distorting or geometrical-optical illusions are characterized by distortions of size, length, position or curvature. A striking example is the Café wall illusion. Other examples are the famous Müller-Lyer illusion and Ponzo illusion. In studying geometry one concentrates on the position of points and on the length, orientation and curvature of lines. Geometrical-optical illusions then relate in the first instance to object characteristics as defined by geometry. Though vision is three-dimensional, in many situations depth can be factored out and attention concentrated on a simple view of a two-dimensional tablet with its x and y co-ordinates. Paradox illusions are generated by objects that are paradoxical or impossible in “real life” or three dimensions, but look oddly convincing and perplexing in two dimensional drawings. Such illusions are often dependent on a cognitive misunderstanding that adjacent edges must join. Lionel Penrose and his son Roger Penrose created several such classic impossible objects as the Penrose Triangle and the Penrose Stairs. The Penrose stairs is a two-dimensional depiction of a staircase in which the stairs make four 90-degree turns as they ascend or descend yet form a continuous loop, so that a person could climb them forever and never get any higher. This is clearly impossible in three dimensions; the two-dimensional figure achieves this paradox by distorting perspective. The best known example of Penrose stairs appears in the lithograph Ascending and Descending by M. C. Escher, where it is incorporated into a monastery.
Figure 2.3 Fictional illusion: The perception of objects that are genuinely not there to all but a single observer usually fictional illusions are induced by something that causes hallucination like alcohol or drugs examples includes seeing two or more of the same object or seeing movement where there is none.
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Literal Illusions Literal optical illusions create images that are completely different from the objects that create them. These tend to be one of the simplest forms of illusions, and as a result less scientific attention is typically given to them. These are the simplest of all and are characterized by, the difference in the image (of what is perceived) and the actual physical objects that make the picture. That is, the picture will give you a different illusion instead of the actual objects in the picture.
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The Visual Mechanism [How We See and the Trained Eye]
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The Eye’s Influence The eye as an optical mechanism is reducible to a single lens and therefore the image focused upon the retina is inverted. However, there is no way for the observer to be conscious of this and therefore the inverted image causes no difficulty in seeing. The images of objects in the right half of the field of view are focused upon the left half of the retina. Similarly, the left half of the field of view corresponds to the right half of the retina; the upper half of the former to the lower half of the latter; and so on. When a ray of light from an object strikes the retina the impression is referred back along the ray-line into the original place in space. This is interestingly demonstrated in a simple manner. Punch a pin-hole in a card and hold it about four inches from the eye and at the same time hold a pin-head as close to the cornea as possible. The background for the pin-hole should be the sky or other bright surface. After a brief trial an inverted image of the pin-head is seen in the hole. Punch several holes in the card and in each will be seen an inverted image of the pin-head. The explanation of the foregoing is not difficult. The pin-head is so close to the eye that the image cannot be focused upon the retina; however, it is in a very favorable position to cast a shadow upon the retina, the light-source being the pin-hole with a bright background. Light streaming through the pin-hole into the eye casts an erect shadow of the pin-head upon the retina, and this erect image is projected into space and inverted in the process by the effect of the lens. The latter is not operative during the casting of the shadow because the pinhead is too close to the lens, as already stated. It is further proved to be outward projection of the retinal image (the shadow) because by multiplying the number of pin-holes (the light-sources).
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The foregoing not only illustrates the inversion of the image but again emphasizes the fact that we do not see retinal images. Even the “stars” which we see on pressing the eye-lid or on receiving a blow on the eye are projected into space. The “motes” which we see in the visual field while gazing at the sky are defects in the eye-media, and these images are projected into space. We do not see anything in the eye. The retinal image impresses the retina in some definite manner and the impression is carried to the brain by the optic nerve. The intellect then refers or projects this impression outward into space as an external image. The latter would be a facsimile of the physical object if there were no optical illusions but the fact that there are optical illusions indicates that errors are introduced somewhere along the path from and to the object. It is interesting to speculate whether the first visual impression of a new-born babe is “projected outward” or is perceived as in the eye. It is equally futile to conjecture in this manner because there is no indication that the time will come when the baby can answer us immediately upon experiencing its first visual impression. The period of infancy increases with progress up the scale of animal life and this lengthening is doubtless responsible and perhaps necessary for the development of highly specialized sense-organs. Incidentally, suppose a blind person to be absolutely uneducated by transferred experience and that he suddenly became a normal adult and able to see. What would he say about his first visual impression? Apparently such a subject is unobtainable. The nearest that such a case had been approached is the case of a person born blind, whose sight has been restored. This person has acquired much experience with the external world through other senses. It has been recorded that such a person, after sight was restored, appeared to think that external objects “touched” the eyes. Only through visual experience is this error in judgment rectified.
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Anatomy of the Eye Hermann von Helmholtz, who contributed much toward our knowledge of the visual process, in referring to the eye, once stated that he could make a much better optical instrument but not a better eye. In other words, the eye is far from an ideal optical instrument but as an eye it is wonderful. Its range of sensitiveness and its adaptability to the extreme variety of demands upon it are truly marvelous when compared with instruments devised by mankind. Obviously, the eye is the connecting link between objective reality and visual perception and, therefore, it plays an important part in optical illusions. In fact, sometimes it is solely responsible for the optical illusion. The process of vision may be divided into several steps such as the lighting, color, character, and disposition of objects; the mechanism by which the image is formed upon the retina; various optical defects of this mechanism; the sensitiveness of the parts of the retina to light and color; the structure of the retina; the parts played by monocular and binocular vision; and the various events which follow the formation of the image upon the retina.
Figure 3.1 Optic Nerve
1
Carries messages from your retina to your brain.
Retina
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Change light into messages that your brain understands.
Lens
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Changes shape to focus light onto your retina.
Cornea
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The curved cornea bends light into your eye.
Pupil
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Changes size to let more or less light into your eye.
Iris
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Muscles that open and close your pupil.
The mechanism of the eye makes it possible to see not only light but objects. Elementary eyes of the lowest animals perceive light but cannot see objects. These eyes are merely specialized nerves. In the human eye the optic nerve spreads to form the retina and the latter is a specialized nerve. Nature has accompanied this evolution by developing an instrument - the eye - for intensifying and defining and the whole is the visual sense-organ. The latter contains the most highly specialized nerve and the most refined physiological mechanism, the result being the highest sense-organ.
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The Visual Mechanism The eye is approximately a spherical shell transparent at the front portion and opaque (or nearly so) over the remaining eighty per cent of its surface. The optical path consists of a series of transparent liquids and solids. The chief details of the structure of the eye are represented in Figure 1. Beginning with the exterior and proceeding toward the retina we find in succession the cornea, the anterior chamber containing the aqueous humor, the iris, the lens, the large chamber containing the vitreous humor, and finally the retina. Certain muscles alter the position of the eye and consequently the optical axis, and focusing (accommodation) is accomplished by altering the thickness and shape, and consequently the focal length. Errors in the mechanism of the eye are a cause of vision disorders. In myopia (nearsightedness), for example, the light does not focus directly on the retina but in front of it. As a result, the image will be out of focus when looking at a distant object. This is generally caused by the eye being elongated or the cornea having the wrong curvature. The error can be compensated by using corrective lenses such as glasses or contact lenses. The same is true with other refractive errors, like hyperopia (farsightedness) where the light focuses behind the retina making close up objects out of focus. However, the cause of a disorder may be in another part of the optic pathway, for example the optic nerve. The iris is a shutter which automatically controls to some degree the amount of light reaching the retina, thereby tending to protect the latter from too much light. It also has some influence upon the definition of the image; that is, upon what is termed “visual acuity� or the ability to distinguish fine detail. It is interesting to compare the eye with the camera. In the case of the camera and the photographic process, we have an inverted light-image, a facsimile of the object usually diminished in size; an invisible image in the photographic emulsion consisting of molecular changes due to light; and a visible image developed on the plate. In the case of the eye and the visual process we have an inverted light-image, a facsimile of the object diminished in size; the invisible image in the retinal substances probably consisting of molecular changes due to light; external visible image. It will be noted that in the case of vision the final image is projected outward - it is external. The more we think of this outward projection the more interesting and marvelous vision becomes. For example, it appears certain that if a photographic plate could see or feel, it would see or feel the silver image upon itself but not out in space. However, this point is discussed further in the next chapter. In the camera and photographic process we trace mechanism, physics, and chemistry throughout. In the eye and visual process we are able to trace these factors only to a certain point, where we encounter the super-physical and super-chemical. At this point, molecular change is replaced by perception, sensation, emotion and thought. Our exploration will take us from the physical world into another, wholly different, where there reigns another order of phenomena. We have passed from the material into the mental world.
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Brain recognizes image
Object
Image inverted in retina
Contributing Effects Man studies his kind too much apart from other animals and perhaps either underestimates or overestimates the amount of inherited, innate, instinctive qualities. A new-born chick in a few minutes will walk straight to an object and seize it. Apparently this implies perception of distance and direction and a coordination of muscles for walking and moving the eyes. It appears reasonable to conclude that a certain amount of the wealth of capacities possessed by the individual is partly inherited, and in man acquired predominates. But all capacities are acquired, for even the inherited was acquired in ancestral experience. Even instinct must involve inherited experience. These glimpses of the depths to which one must dig if he is to unearth the complete explanations of visual perception Consequently of optical illusions indicate the futility of treating the theories in the available space without encroaching unduly upon the aims of this volume. Certain defects of the optical system of the eye must contribute toward causing optical illusions. Any perfect lens of homogeneous material has at least two defects, known as spherical and chromatic aberration. The former manifests itself by the bending of straight lines and is usually demonstrated by forming an image of an object such as a wire mesh or checker-board; the outer lines of the image are found to be very much bent. This defect in the eye-lens is somewhat counteracted by a variable optical density, increasing from
the outer to the central portion. This results in an increase in refractive-index as the center of the lens is approached and tends to diminish its spherical aberration. The eye commonly possesses abnormalities such as astigmatism and eccentricity of the optical elements. All these contribute toward the creation of optical illusions. White light consists of rays of light of various colors and these are separated by means of a prism because the refractive-index of the prism differs for lights of different color or wave-length. This causes the blue rays, for example, to be bent more than the red rays when traversing a prism. It is in this manner that the spectrum of light may be obtained. A lens may be considered to be a prism of revolution and it thus becomes evident that the blue rays will be brought to a focus at a lesser distance than the red rays; that is, the former are bent more from their original path than the latter. This defect of lenses is known as chromatic aberration and is quite obvious int the eye. It may be demonstrated by any simple lens, for the image of the sun, for example, will appear to have a colored fringe. A purple filter which transmits only the violet and red rays is useful for this demonstration. By looking at a lamp-filament or candle-flame some distance away the object will appear to have a violet halo, but the color of the fringe will vary.
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Figure 3.2 The human eye and how images are formed in the retina. Note that the images are upside-down. An important question to consider: does the human brain come pre-wired to turn the inverted image around or does the brain learn how to invert images?
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Figure 3.3 The Blindspot exposure. Close your left eye and look at the cross with you right eye. As you look at the cross move the page forward and backward until the dot disappears. What do you see in each example?
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On looking through a pin-hole at the edge of an object silhouetted against the bright sky the edge will appear red if the light from the pin-hole enters the pupil near its periphery. This optical defect of the eye makes objects appear more sharply defined when viewed in monochromatic light. In fact, this is quite obvious when using yellow glasses. The defect is also demonstrated by viewing a line-spectrum focused on a ground glass. The blue and red lines cannot be seen distinctly at the same distance. The blue lines can be focused at a much less distance than the red lines. Chromatic aberration can account for such an optical illusion as the familiar “advancing” and “retiring” colors and doubtless it plays a part in many optical illusions. The structure of the retina plays a very important part in vision and accounts for various optical illusions and many interesting visual phenomena. The optic nerve spreads out to form the retina which constitutes the inner portion of the spherical shell of the eye with the exception of the front. The place where the optic nerve enters the eyeball and begins to spread out is blind. Objects whose images fall on this spot are invisible. This blind-spot is not particularly of interest here, but it may be of interest to note its effect. This is easily done by closing one eye and looking directly at one of two small black circles about two inches apart on white paper at a distance of about a foot from the eye. By moving the objects about until the image of the circle not directly looked at falls upon the blind-spot, this circle will disappear. A three-foot circle at a distance of 36 feet will completely disappear if its image falls directly upon the blind-spot. At a distance of 42 inches the invisible area is about 12 inches from the point of sight and about 3 to 4 inches in diameter. At 300 feet the area is about 8 feet in diameter. The actual size of the retinal blind-spot is about 0.05 inch in diameter or nearly 5 degrees. Binocular vision overcomes any annoyance due to the blind-spots because they do not overlap in the visual field. A one-eyed person is really totally blind for this portion of the retina or of the visual field.
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Mind Power [Optical Illusion’s Affect on the Brain]
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Optical Illusion and the Mental The eyes are an extension of the brain. The connection between brain activity and vision is really quite vast. Light affects the brain through the eyes. Our eyes charge and energize our brain and nervous system. The light coming in through the eyes can augment the function of the nervous and vision system. While medical science has shown that light has a profound stimulatory and regulatory effect on all of the body’s vital functions, phototherapy has found that specific portions of the visible spectrum act as the rebalancers of these vital functions. Light may well be the major nutrient which feeds the evolution of all life.
The health of a person is not only associated to how well his body functions but also to how well are his psychological and emotional states. Optical illusion images and visual effects can have a strong effect on emotional state and partially or entirely can changes the psychological or physical functioning of individuals by Self-Regulation. Our brain is looking for ways to maintain or restore a balanced state. When people look at suitable optical illusion images, it is providing self-regulation by using their own mechanisms of the health support. Optical illusions are a very wonderful way of supporting people’s health and wellness.
The modern idea of Self-Regulation as a healing influence is based on the prescribed use of light and color to effect positive changes in the psychological or physical functioning of individuals. Humans need light of specific intensity and color range to regulate their biological states. The different light affects and controls human being and biological processes in the nature. Color has a profound effect on us on all levels physical, mental, emotional and spiritual.
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Perception
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Figure 4.1
How information is perceived depends also on learned perceptions. For example, people who have spent their lives in a dense forest have difficulty judging distance and size in large open areas like the prairies. They do not realize that objects that are large may appear small because they are far away. Although their vision is sharp, their perception of the world is inaccurate. What they have learned about interpreting the information provided by their senses is incomplete. People’s perceptions can be fooled when seeing something that lies outside their previous experience. When looking at optical illusions, the eyes are recording an image that the brain misinterprets. The brain likes to group things into patterns of familiar forms. It is always comparing things with its experience and knowledge of the world. For example, the brain knows that a bicycle wheel is circular. So even though the wheel may not look circular from a particular angle or perspective, the brain interprets the wheel as circular.
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Frontal Lobe
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This lobe is responsible for your deeper thinking.
Temporal Lobe
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These regions are involved in helping you recognize objects.
Brain Stem
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Controls the things that happen automatically in you body.
Parietal Lobe
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They tell you what you feel and alert your body.
Occipital Lobe
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Process all signals sent from your eyes to give you sight.
Cerebellum
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Organizes signals sent out to muscles so movements are smooth.
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Visual Effects for Mental Health The different abilities of our brain are involved in our vision creativity. However, human perception is defined by the dissociation between physical reality and subjective perception. We never have 100% of the information to make correct deciding. People like to have the illusions, as illusions aren’t just comforting they improve health. Our separation from each other is an illusion of consciousness. The dictionary defines reality as something that is in a state of being actual or true. However, reality is different due to perception and the differences in our brains. Optical illusion is a phenomenon that confirm this fact. Optical illusions appear when our brain misunderstands the visual stimulus, which has taken into by our eyes. Optical illusions it’s caused by how our brain functions.
Figure 4.2 The brain has a strong neural response when center is bright, surrounded by dark. The graph depicts how the brain stimulus is activated when looking at brighter areas. Areas that are surrounded by a darker color cause the most stimulus to occur.
Optical illusions may consist of the unique color compositions, which can change the human perception of the reality. Optical illusion has been known since antiquity. Until now, mostly the optical illusion images has been considered as tricks, puzzles, art for fun etc. However it is only one aspect of what optical illusion give us. Other aspect, optical illusion have therapeutic effects on human beings. An optical illusion or visual illusion appear when our brain misunderstands the visual stimulus, which has taken into by our eyes. It is happens when the visual effects on the eyes and brain have a specific brightness, oscillation frequencies, color, movement etc. The optical illusions and visual effects can have a strong effect on emotional and physical states of the human beings. Strength of an visual illusion and effects relies on the perception of the illusion by visual sensory interactions with brain. Our brain is looking for ways to maintain or restore a balanced state. You will find yourself drawn to one optical illusion more than to others. Suitable optical illusion for you is the one you need at this moment. When people look at suitable optical illusion and visual effects, such illusion to promote self-regulation and develop their own mechanisms of the emotional support and health protection. Stimulus
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Figure 4.3 Some say that color effects have therapeutic value. Stare at the image for at least a minute. Watch as the lines jittery a around the circle, as the circles move up and down the line. Even weirder, most people see an alteration in the color of the circle after a few moments of intense staring.
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Optical Illusion Disorders How can something not actually there, be seen incorrectly? It all amounts to a neurophilosophical nightmare from which a pragmatic clinical escape route is to pool illusions and hallucinations into a single entity the ‘positive’ disorders of visual perception treating both alone. But loosening definitions with one hand requires tightening them with the other. All reports of ‘seeing things’ need not indicate a positive perceptual disorder. Before diving deep into the patient’s visual psyche, it is worth pausing to consider whether the symptom being described is vivid visual imagery. Visual images appear in the mind’s eye and are under some degree of volitional control, as opposed to hallucinations and illusions which are externally located, unpredictable and outside volition (in the sense that one cannot choose to make a hallucination of, say, a face turn into that of a chair). Termed pseudohallucinations in the European psychopathological tradition, vivid visual images carry very different aetiological implications to those of hallucinations and illusions,imagery pointing to a diagnostic spectrum which ranges from normal phenomena to clinical anxiety syndromes. Note that, confusingly, the American psychopathological tradition uses the term pseudohallucination in a different way, referring to hallucinations that are recognized for what they are.
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Micropsia Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. Micropsia can be caused by optical factors (such as wearing glasses), by distortion of images in the eye (such as optically, via swelling of the cornea or from changes in the shape of the retina such as from retinal edema, macular degeneration, or central serous chorioretinopathy), by changes in the brain (such as from traumatic brain injury, epilepsy, migraines, prescription drugs, and illicit drugs), and from psychological factors. Dissociative phenomena are linked with micropsia, which may be the result of brain lateralization disturbance. Micropsia is also commonly reported when the eyes are fixating at convergence, or focusing at accommodation, a distance closer than that of the object in accord with Emmert’s law. Specific types of micropsia include hemimicropsia, a form of micropsia that is localized to one half of the visual field and can be caused by brain lesions in one of the cerebral hemispheres. Related visual distortion conditions include macropsia, a less common condition with the reverse effect, and Alice in Wonderland Syndrome, a condition that has symptoms that can include both micropsia and macropsia. Micropsia causes affected individuals to perceive objects as being smaller or more distant than they actually are.
Figure 4.4 The Ebbinghaus illusion consists of a circle surrounded in one image by smaller circles, and in another by larger circles. The viewer tends to perceive the circle surrounded by smaller circles as being larger than the circle in the other image, even though both are exactly the same size.
The majority of individuals with micropsia are aware that their perceptions do not mimic reality. Many can imagine the actual sizes of objects and distances between objects. It is common for patients suffering from micropsia to be able to indicate true size and distance despite their inability to perceive objects as they actually are. One specific patient was able to indicate the dimensions of specific objects with her hands. She was also able to estimate the distances between two objects and between an object and herself. She succeeded in indicating horizontal, vertical, and 45 degree positions and did not find it difficult to search for an object in a cluttered drawer, indicating that her figure-ground discrimination was intact despite suffering from micropsia. Individuals experiencing hemimicropsia often complain that objects in their left or right visual field appear to be shrunken or compressed. They may also have difficulty appreciating the symmetry of pictures. When drawing, patients often have a tendency to compensate for their perceptual asymmetry by drawing the left or right half of objects slightly larger than the other. In a case of one person with hemimicropsia asked to draw six symmetrical objects, the size of the picture on the left half was on average 16% larger than the corresponding right half.
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Your m way ah of you.
mind is head .
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BIBLIOGRAPHY
Association for Research in Vision and Ophthalmology. “Not Just Your Imagination: Brain Perceives Optical Illusions As Real Motion.” ScienceDaily. ScienceDaily, 3 February 2009.
Eagleman, David M. “Visual Illusions and Neurobiology.” Visual Illusions and Neurobiology (2001): 1-7. Macmillan Magazines Ltd, 1 Dec. 2001. Web. 9 Dec. 2014.
Bach, Michael, and Charlotte M. Poloschek. Advances in Clinical Neuroscience & Rehabilitation Journal 3.112 (2006): 63-64. Advances in Clinical Neuroscience &Rehabilitation. ACNR, 1 May 2006. Web. 14 Oct. 2014.
Fermuller, Cornelia R, and Henrik Malm. “Uncertainty in Visual Processes Predicts Geometrical Optical Illusions.” Vision Research (2001): n. pag. Science Direct, 8 June 2001. Web. 24 Nov. 2014.
Betancourt, Michael. “Precision Optics / Optical Illusions: Inconsistency, Anemic Cinema, and the Rotoreliefs.” Tout Fait, 2 Apr. 200. Web. 3 Dec. 2014.
Gupta, Mohit. “Optical Illusions.” Understanding Optical Illusions 17.5 (2000): 1-49. 1 Mar. 2006. Web. 5 Nov. 2014.
Bryner, Jeanna. “Key to All Optical Illusions Discovered.” LiveScience. TechMedia Network, 02 June 2008. Web. 15 Dec. 2014.
Hoffman, Donald D. “Visual Illusions and Perception.” Visual Illusions and Perception (2005): n. pag. University of California Irvine, 1 Feb. 2005. Web. 11 Dec. 2014.
Cline, Jennifer. “Optical Illusions and Your Brain.” Optical Illusions and Your Brain. Helix, 9 Oct. 2009. Web. 8 Dec. 2014.
Lewis, Tanya. “Optical Illusion Explained in Monkey Brain Study.” LiveScience. TechMedia Network, 30 Sept. 2013. Web. 15 Dec. 2014.
“Exploring Optical Illusions.” Types Of Optical Illusions -. N.p., 15 July 2008. Web. 24 Nov. 2014.
Ffytche, Dominic. “Visual Hallucinations And Illusions With Propranolol.” Advances in Clinical Neuroscience & Rehabilitation Journal 1.6121 (2004): 1182. Advances in Neuroscience & Rehabilitation. ACNR, 1 May 2004. Web. 24 Nov. 2014.
Lo, Ka C. “Research.” Reproductive Health Matters 20.40, Sexual and Reproductive Morbidity: Not a Priority (2012): 223-24.Investigation of Optical Illusions on the Aspects of Gender and Age. The UCLA Undergraduate Science Journal, Apr. 2012. Web. 2 Dec. 2014.
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Luckiesh, Matthew. “Visual Illusions: Their Causes, Characteristics and Application 2014. s.” Visual Illusions: Their Causes, Characteristics and Applictions. N.p., 1996. Web. 24 Nov. 2014.
Speert, Debra. “Sensory Illusions.” BrainFacts. N.p., 1 Oct. 2011. Web. 15 Dec. 2014. Wolchover, Natalie. “The Most Amazing Optical Illusions (and How They Work).” Live Science. TechMedia Network, Aug. 2011. Web. 15 Dec. 2014.
Nierenbergabc, Cari. “Optical Illusions: When Your Brain Can’t Believe Your Eyes.” ABC News. ABC News Network, 13 Oct. 2009. Web. 1 Dec. 2014. Oliver, Sarah.
“Optical Illusions and Their Causes: Examining Differing Explanations.” Olin College of Engineering, 4 Jan. 2006. Web. 24 Nov. 2014.
Woloszyn, Michael R. “Contrasting Three Popular Explanations for the Muller-Lyer Illusion.” Current Research in Psychology 1.2 (2010): 102-07. Science Publications, 25 Feb. 2001. Web. 18 Nov. 2014. Zyga, Lisa. “Optical Illusions: Caused by Eye or Brain?” Optical Illusions: Caused by Eye or Brain? N.p., 11 Nov. 2008. Web. 24 Nov. 2014.
“Optical Illusion.” Optical Illusion. N.p., June 2008. Web. 24 Nov. 2014. “Optical Illusions Further Explained - Optical Illusions Pictures.” Optical Illusions Pictures. N.p., 7 Feb. 2002. Web. 15 Dec. 2014. “Optical Illusion Images and Visual Effects for Mental Health.” Optical Illusion Images and Visual Effects for Mental Health. N.p., 2011. Web. 24 Nov. 2014. Seckel, Al. “Visual Illusions That Show Us How We (Mis)Think.” TED. N.p., Feb. 2004. Web. Nov.-Dec. 2014.
Segall, Marshall H., Donald T. Campbell, and Melville J. Herskovit. The Influence of Culture on Visual Perception (n.d.): n. pag. 1968. Web. 6 Nov. 2014.
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COLOPHON
This book was set in Apercu and Baskerville typefaces. The text is set in Baskerville designed by John Baskerville in England in the mid-18th century. The sub-text and headings are set in Apercu. It was designed by UK-based type foundry The Entente in 2010. Adobe InDesign, Illustrator, & Photoshop
Apercu Type sizes used: 6pt, 8pt, 9pt, 28pt, 4pt Weights used: Regular, mono, light italic, bold Baskerville
iMac desktop 21.5-inch: 2.7 GHz Canon Pixma iX6800 Series Printer
Type sizes used: 9pt
Epson Heavyweight Matte Five Star Weights used: Regular
Printing & Binding: Plotnet, San Francisco, Ca Date: December 15, 2014 MIT Press, Cambridge, Massachusetts Designed by Nic Arnado Photographs: Stock Images Illustrations: thenounproject.com This is a student project only. No part of this book or any other part of the project was produced for commercial use.
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